The present invention relates, in general, to electronics, and more particularly, to semiconductors, structures thereof, and methods of forming semiconductor devices.
In the past, solar powered garden lights typically charged a battery from a solar cell during daylight conditions, and then used the charged battery to power an LED during nighttime conditions. The battery was typically charged by coupling the battery to the solar cell through a diode or a diode-connected transistor. The diode or diode-connected transistor introduced a voltage drop of about 0.7 Volts, which reduced the efficiency of the battery charging operation. Moreover, leakage through the diode or diode-connected transistor often reduced the efficiency of the charging operation.
The decision to power the LED usually was typically made in response to comparing the battery voltage with a voltage from a photo resistor. This comparison undesirably required a comparator, which usually was continuously powered from the battery, thereby undesirably increasing the power requirements of the system and reducing the efficiency of charging the battery. Additionally, the photo-resistor often was another system element which increased the costs.
The LED was typically powered by charging an inductor during one phase of a clock signal, and then discharging the inductor to supply current to the LED during another phase of the clock signal. The current flow to the LED was controlled by controlling the pulse width of the phases of the clock signal. However, the required pulse width modulation circuitry was fairly complex, and resulted in significant power consumption.
A capacitor often typically was connected in parallel with the LED, such that the capacitor was charged during the time that the inductor discharged to power the LED. The charged capacitor could then supply the LED during the period while the inductor was subsequently recharged. However, during the inductor discharge phase, it was possible that the inductor may remain electrically connected to the LED and capacitor after the inductor had been completely discharged. Under such conditions, charge could undesirably flow from the capacitor back into the inductor (reverse charge flow) at the end of the discharge phase.
It would therefore be desirable to have an improved solar powered garden light that operates more efficiently than conventional solar-powered lights, and that has a lower cost.
For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, or certain N-type or P-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein relating to circuit operation are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action. The use of the word approximately or substantially means that a value of an element has a parameter that is expected to be very close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to at least ten percent (10%) are reasonable variances from the ideal goal of exactly as described.